1. Field of the Invention
This invention relates to the preparation of modified polystyrene polymers and is more particularly concerned with processes for the preparation of organo-arsenic derivatives of polystyrene and related compounds.
2. Description of the Prior Art
Organo-arsenic derivatives of polystyrene and related compounds have recently been shown to be highly active as catalysts for the conversion of organic isocyanates to the corresponding carbodiimides; U.S. Pat. Nos. 4,098,973 and 4,143,063. The preparative procedures for these polymeric catalysts hitherto described have involved reacting the appropriate polystyrene having a bromo or chloromethyl substituent in at least some of the aromatic nuclei in the polymer chain, with the appropriate dihydrocarbylarsine halide in the presence of metallic lithium. The resulting polymer, having dihydrocarbylarseno substituents in at least some of the aromatic nuclei in the chain, is then oxidized, using hydrogen peroxide or like oxidizing agents, to the corresponding As-oxides which are the polymeric catalysts described in the above cited patents.
The above process has the disadvantage that the dihydrocarbylarsine halides employed as reactants are extremely costly to prepare and this is reflected in the cost of the final polymeric catalysts themselves.
However, in view of the very valuable advantages possessed by the above polymeric catalysts in the preparation of carbodiimides and particularly in the preparation of carbodiimide-containing diisocyanates as set forth in U.S. Pat. No. 4,143,063, supra, it was highly desirable to devise more economical methods for the preparation of these polymeric catalysts. We have now found that these catalysts can be prepared readily by a novel process which involves the use of the relatively inexpensive arsenic trihalides or arsenic trioxide in place of the highly expensive dihydrocarbylarsine halides.